Cap at resistors of electrical test probe

ABSTRACT

A lossy dielectric device dissipates, absorbs, and/or dampens electric fields. The lossy dielectric device may be used with any transmission path, such as a transmission line or resistor in a probe head. The lossy dielectric device preferably includes a lossy dielectric material contained within a container. The container is positionable and securable substantially adjacent the transmission path to improve the curve of a frequency response. Preferably, the container is insulative, puncture resistant, and thin. In some preferred embodiments, a temporary or permanent connection mechanism is also included.

The present application is a continuation of U.S. patent applicationSer. No. 11/018,134, filed Dec. 17, 2004, now U.S. Pat. No. ______. U.S.patent application Ser. No. 11/018,134 is an application claiming thebenefit under 35 USC Section 119(e) of U.S. Provisional PatentApplication Ser. No. 60/531,077, filed Dec. 18, 2003. The presentapplication is based on and claims priority from these applications, thedisclosures of which are hereby expressly incorporated herein byreference.

BACKGROUND OF INVENTION

The present invention is directed to a lossy dielectric cap thatdissipates electric fields that may be used near current transmission orconduction paths in a probing head of an electrical test probe.

FIG. 1 shows a probing system that includes an electrical test probe 20for providing an electrical connection between electrical components 22and testing instruments 24. An electrical test probe 20 generallyconsists of a probing head 30, a cable 32, and a testing instrumentconnector 34. The probing head 30 may have an integral or replaceableprobe tip 40 that is suitable for making an electrical contact withelectrical components 22. The testing instrument connector 34 issuitable for connecting to a testing instrument 24. If the probe tip 40is replaceable, generally the probing head 30 will have a socket 38 orother connection mechanism for mating with the probe tip 40. The probinghead 30 is attached to a first end of the cable 32 and the testinginstrument connector 34 is attached to the opposite end of the cable 32.

As current flows through wires and electrical components, it generateselectromagnetic fields. Some of the energy radiates around the wires andelectrical components. At certain frequencies, the fields can reflectand bounce back into the wires and electrical components. This processtends to create a varying response with respect to frequency that isundesirable. Ideal test probes have a perfect curve frequency response(shown as a flat line on a frequency response graph) in which voltage inis equal to (or proportional to) voltage out.

FIG. 2 shows a frequency response graph of the exemplary 7.5 GHzbandwidth probe shown in FIG. 3. This exemplary probe has adjustabledual tip technology that allows the user to set the spacing of the probetips in a continuously variable fashion. Within its housing 48, theprobe head 30 in FIG. 3 includes a crisscross spring with a “u” shapedover molded on the free ends of the spring 50 a, 50 b. The probe head 30has an elongated cast shell 52 that houses the bulk of a hybrid 54 witha custom amplifier. The 50-Ohm transmission line input 56 a, 56 b, 56 ccomes out of the elongated housing, arches up, splits at a 90 degreeangle and bends into the “u” shaped channels where they are fixed orglued. A thin 0.020″ FR4 backer 58 backs the flex. As the backer 58emerges from the “u,” a resistor 60 is in series with the transmissionline 62 and tip 40. A small notch 64 on the FR4 backer 58 accommodates agrounding tether 66. The grounding tether 66 may be soldered orotherwise attached between the series resistor 60 and the 50-Ohmtransmission line 56 a, 56 b, 56 c. The 7.5 GHz bandwidth rating istypical for the probe as a stand-alone device. As an ideal frequencyresponse is flat, the large increase in signal amplitude at highfrequencies (peaking) shown in FIG. 2 would be understood as undesirablein a frequency response.

Much of the undesired variation in frequency response is due to the factthat some electromagnetic energy radiates into space from the probetips. This energy can couple back onto the probe circuitry after theattenuating resistor, increasing or decreasing the signal leveldepending on the phase of the radiated path.

It has long been known that ferrite material (e.g. ferrite caps) can beused to dissipate, absorb, and/or dampen magnetic fields. In theexemplary probe head 30 of FIG. 3, ferrite material is shown as 68.Ferrite materials attempt to resolve problems associated with magneticfields. When placed near metal conductors, these materials can attenuatethe magnetic fields created by high frequency current flow, and thusreduce radiated fields. One problem with the ferrite materials is thatthey do not solve the problems associated with electrical fields.Another problem with the ferrite materials is that since they are placednear conductors to dampen the magnetic fields, they can also change theelectrical characteristics of the conductors. For example, placing aferrite bead around a probe tip will increase the tip inductance at thesame time as reducing the radiated field. Test probes with ferritematerials do not have perfect frequency responses.

Other material such as conductive foam (e.g. foam with slightlyconductive properties), and conductive films, have also been used forsolving problems with electromagnetic fields. None of these productshave provided satisfactory results.

BRIEF SUMMARY OF THE INVENTION

It is desirable to have a material that would dissipate, absorb ordampen electric fields so that such material could be placed and securedin positions where the electric field is stronger, and reduce undesiredsignals.

The present invention is directed to a lossy dielectric device for usewith a transmission path, such as a transmission line or resistor in aprobe head. The lossy dielectric device preferably includes a lossydielectric material contained within a container. The container ispositionable and securable substantially adjacent said transmission pathto improve the curve of a frequency response. Preferably, the containeris insulative, puncture resistant, and thin. In some preferredembodiments, a temporary or permanent connection mechanism is alsoincluded.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary probing system in whichthe present invention may be used.

FIG. 2 is a frequency response graph an exemplary test probe.

FIG. 3 is a cross-sectional side view of an exemplary prior art testprobe having ferrite material.

FIG. 4 is a frequency response graph an exemplary test probe with auser's finger held over the resistors.

FIG. 5 is a cross-sectional side view of a first exemplary lossydielectric cap of the present invention in which the container has asemi-rigid bottom surface and a soft upper surface.

FIG. 6 is a perspective view of the first exemplary lossy dielectric capshown in FIG. 5.

FIG. 7 is a cross-sectional side view of a second exemplary lossydielectric cap of the present invention in which the container iscompletely soft.

FIG. 8 is a cross-sectional side view of a third exemplary lossydielectric cap of the present invention in which the container has anintegral or added bottom surface.

FIG. 9 is a cross-sectional side view of a fourth exemplary lossydielectric cap of the present invention in which the container has anintegral or attached bottom surface with at least one protrusion formating with probe structure.

FIG. 10 is a cross-sectional side view of a fifth exemplary lossydielectric cap of the present invention in which the container hasformed bottom surface that may be used to mate with components of theprobing head.

FIG. 11 is a cross-sectional side view of a sixth exemplary lossydielectric cap of the present invention.

FIG. 12 is a cross-sectional side view of an exemplary test probe withan exemplary lossy dielectric cap positioned on the front of the probinghead housing behind the tip and resistors.

FIG. 13 is a perspective view of an exemplary test probe with anexemplary lossy dielectric cap positioned inside of the probing headhousing.

FIG. 14 is a perspective view of an exemplary test probe with anexemplary lossy dielectric cap positioned on the front of the probinghead housing behind the tip and resistors.

FIG. 15 is a perspective view of an exemplary test probe with anexemplary lossy dielectric cap positioned behind the tip PCA oppositethe resistors.

FIG. 16 is a cross-sectional side view of an exemplary test probe withan exemplary lossy dielectric cap positioned along the transmission pathinside the probing head housing.

FIG. 17 is a cross-sectional side view of an exemplary test probe withan exemplary lossy dielectric cap positioned along the transmission pathinside the probing head housing.

FIG. 18 is a cross-sectional side view of an exemplary test probe withan exemplary lossy dielectric cap positioned along the transmission pathinside the probing head housing.

FIG. 19 is a frequency response graph the exemplary test probe of FIGS.12 and 13.

FIG. 20 is a frequency response graph the exemplary test probe of FIG.15.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1 the present invention may be implemented as part of aprobing system that includes an electrical test probe 20 for providingan electrical connection between electrical components 22 and testinginstruments 24. An electrical test probe 20 generally consists of aprobing head 30, a cable 32, and a testing instrument connector 34. Theprobing head 30 may have an integral or replaceable probe tip 40 that issuitable for making an electrical contact with electrical components 22.The testing instrument connector 34 is suitable for connecting to atesting instrument 24. If the probe tip 40 is replaceable, generally theprobing head 30 will have a socket 38 or other connection mechanism formating with the probe tip 40. The probing head 30 is attached to a firstend of the cable 32 and the testing instrument connector 34 is attachedto the opposite end of the cable 32.

FIG. 3 shows an exemplary prior art probing head 30. As set forth in thebackground, the probe head 30 includes a resistor 60 is in series with atransmission line 62 and tip 40. The inventor of the present inventionrealized that by placing a finger over the resistors 60, she was able toimprove the frequency curve as shown in FIG. 4. As an ideal frequencyresponse is flat, the reduced peaking shown in FIG. 4 would beunderstood as a more desirable frequency response than the frequencyresponse of the probing head 30 (FIG. 2). The problem is that it wouldbe impossible for a user to hold a finger over the resistors 60permanently.

The present invention contemplates the use of a lossy dielectric capdevice 100 at or near the resistors 60 and/or transmission line 62 of aprobing head 30. The lossy dielectric cap 100 is preferably made frommaterials having a finite conductivity in which the electromagneticfields can propagate, but lose energy. The conductivity should not be solow that the material functions as an insulator through which theelectromagnetic fields would propagate with no attenuation. Theconductivity should not be so high that the material functions as a goodconductor from which the electromagnetic fields would be reflected back.In one preferred embodiment the lossy dielectric cap device 100approximates the composition of a human finger.

FIGS. 5-11 show exemplary embodiments of a lossy dielectric cap 100 ofthe present invention. FIGS. 12-18 show exemplary placements of a lossydielectric cap 100 of the present invention. These figures will bediscussed in more detail below.

Exemplary Embodiments of the Lossy Dielectric Cap

As shown in FIGS. 5-10, the lossy dielectric cap 100 a-e (discussedgenerally as 100) of the present invention preferably includes acontainer 102 a-e (discussed generally as 102) and dielectric material104 a-e (discussed generally as 104) contained within the container. Thecontainer is shaped and/or has connection mechanisms 106 a-e (discussedgenerally as 106) such that the lossy dielectric cap 100 is positionableand securable substantially adjacent the at least one resistor 60 and/orthe transmission line 62 (which may jointly be referred to as atransmission path) of a probing head 30. When correctly positioned thelossy dielectric cap 100 improves the curve of a frequency response of atest probe.

For most of the exemplary embodiments discussed herein, the lossydielectric cap 100 includes a container 102 and dielectric material 104(e.g. a dipole). It should be noted, however, that alternativeembodiments could include any material that has a finite conductivitysuch that the electromagnetic field energy is dissipated.

The container 102 may be made constructed of materials including, butnot limited to plastic, rubber, polymeric material, biologicallycompatible elastically deformable material, that is preferablyinsulative, puncture resistant, and thin. The container 100 may be allor partially flexible, may be semi-rigid or contain a semi-rigidcomponent, or may be all or partially rigid (if properly formed).

The dielectric material 102 may be made constructed of materialsincluding, but not limited to a saline solution, a polysiloxane or asilicone gel, bio-osmotic gel (e.g. such as the combination of abio-compatible organic polymer and a solution of bio-compatible saltdisclosed in U.S. Pat. No. 5,067,965 to Ersek, which is incorporatedherein by reference), or any lossy dielectric material. The dielectricmaterial 102 would most likely be an organic material. One exemplarydielectric material 102 would be a mixture that includes the followingingredients: buffered, isotonic liquid solution of a borate buffersystem and sodium chloride, sorbic acid, and edentate disodium.

It should be noted that the connection mechanism 106 for connecting thelossy dielectric cap 100 to a probe may be integral with the probe.Alternatively, connection mechanism 106 for connecting the lossydielectric cap 100 may be temporarily or permanently attachable toand/or removable from the probe. As an example of an integral connectionmechanism 106, the housing 48 of a probe may include an integralcompartment that functions as a container 102. An adhesive may be usedas a temporary connection mechanism 106 or as a permanent connectionmechanism 106. For example, if a temporary, semi-permanent, or removableadhesive (e.g. 3M #486 adhesive) is used as the connection mechanism 106then the lossy dielectric cap 100 may be placed/secured in position and,if desired, removed later. Such an adhesive would allow a user toremove, replace, and/or reposition the lossy dielectric cap 100. Thischaracteristic would make the lossy dielectric cap 100 removablyinterconnectable. Preferably, the temporary connection mechanism wouldnot leave a residue when it is removed. If a permanent adhesive (e.g.epoxy or acrylate adhesive) is used as the connection mechanism 106 thenthe lossy dielectric cap 100, once placed, could not be removed.Mechanical mechanisms may also be used either as a temporary connectionmechanism 106 or as a permanent connection mechanism 106.

FIGS. 5-11 show exemplary embodiments of the lossy dielectric cap 100.These embodiments are meant to be exemplary and are not meant to limitthe scope of the present invention.

FIGS. 5 and 6 show a first exemplary lossy dielectric cap 100 a of thepresent invention. This embodiment includes a container 102 a anddielectric material 104 a contained within the container 102 a. Thecontainer 102 a has a semi-rigid bottom surface 110 and a soft,formable, flexible, and/or “squishy” upper surface 112. The connectionmechanism 106 a is adhesive (temporary or permanent) that can secure thelossy dielectric cap 100 a substantially adjacent the at least oneresistors 60 and/or transmission line 62 of a probing head 30.

FIG. 7 shows a second exemplary embodiment of the lossy dielectric cap100 b of the present invention. This embodiment preferably includes acontainer 102 b and dielectric material 104 b contained within thecontainer 102 b. In this embodiment, the container 102 b is completelysoft, formable, flexible, and/or “squishy.” Because of the consistencyof the container 102 b, the lossy dielectric cap 100 b of thisembodiment can be wedged into a tight space and held in position.Accordingly, the container 102 b itself is the connection mechanism 106b that holds the lossy dielectric cap 100 b substantially adjacent theat least one resistor 60 and/or transmission line 62 of a probing head30.

FIG. 8 shows a third exemplary lossy dielectric cap 100 c of the presentinvention. This embodiment includes a container 102 c and dielectricmaterial 104 c contained within the container 102 c. The container 102 chas an integral or added bottom surface 114 a that extends on both sidesbeyond the main compartment of the container 102 c. In this embodimentthe edges of the bottom surface 114 a may mate with probe structure 116a (shown as a pair of jaws or rails that hold the bottom surface 114 aedges) to jointly function as the connection mechanism 106 c to securethe lossy dielectric cap 100 c substantially adjacent the at least oneresistor 60 and/or transmission line 62 of a probing head 30. Oneadvantage of this embodiment is that the bottom surface 114 a may bemade of a ferrite material (a layer of ferrite material) that can beused to dissipate, absorb, and/or dampen magnetic fields.

FIG. 9 shows a fourth exemplary lossy dielectric cap 100 d of thepresent invention. This embodiment includes a container 102 d anddielectric material 104 d contained within the container 102 d. Thecontainer 102 d has an integral or added bottom surface with at leastone protrusion 114 b. In this embodiment the protrusions 114 b may matewith probe structure 116 b (shown as apertures through which theprotrusions 114 b may be inserted) to jointly function as the connectionmechanism 106 d to secure the lossy dielectric cap 100 d substantiallyadjacent the at least one resistor 60 and/or transmission line 62 of aprobing head 30. One advantage of this embodiment is that it may besuspended “upside-down” on top of the resistors 60 and/or transmissionline 62.

FIG. 10 shows a fifth exemplary lossy dielectric cap 100 e of thepresent invention. This embodiment includes a container 102 e anddielectric material 104 e contained within the container 102 e. Thecontainer 102 e has formed bottom surface 118 that may be used to matewith components of the probing head 30.

As shown in FIG. 11, an alternative lossy dielectric cap 150 uses a“solid” dielectric material 154. The dielectric material 154 may befoam, gel, clay, or other material that is soft, “squishy,” or formable.This embodiment eliminates the need for a container. The dielectricmaterial 154 is shaped and/or has connection mechanisms 156 such thatthe lossy dielectric cap 150 is positionable substantially adjacent theat least one resistor 60 and/or transmission line 62 of a probing head30. When correctly positioned the lossy dielectric cap 150 improves thecurve of a frequency response of a test probe.

Exemplary Placements of the Lossy Dielectric Cap

As set forth above, FIGS. 12-18 show exemplary placements of a lossydielectric cap of the present invention. Ideally, the lossy dielectriccap is placed within approximately 0.10 inches (substantially adjacent)of the resistor(s) 60, the transmission line 62, or any other elementsof the transmission path of the probe. These placements, however, aremeant to be exemplary and are not meant to limit the scope of theinvention.

As shown in FIG. 12, in a preferred embodiment a lossy dielectric cap100 may be positioned and secured on the front of the probing head 30housing 48 behind the tip 40 and resistors 60 and/or transmission line62. In the shown embodiment, the dielectric cap 100 is positioned behindthe ground wire 66. In the embodiment shown in FIG. 12 the dielectriccap 100 c (FIG. 8) is used. As can be seen from FIG. 19, this placementof the lossy dielectric cap has a frequency response that is asignificant improvement over the frequency response (FIG. 2) of anexemplary test probe and that roughly approximates the frequencyresponse (FIG. 4) of an exemplary test probe with a user's finger heldover the resistors 60.

As shown in FIG. 13, in a preferred embodiment a lossy dielectric cap100 may be positioned and secured inside of the probing head 30 housing48 behind the tip 40 and resistors 60 and/or transmission line 62. Inthe shown embodiment, the dielectric cap 100 is positioned behind theground wire 66. In this embodiment the dielectric cap 100 a (FIGS. 5 and6) is used.

As shown in FIG. 14, in a preferred embodiment a lossy dielectric cap100 may be positioned and secured in front of the ground wire 66.

As shown in FIG. 15, in a preferred embodiment a lossy dielectric cap100 may be positioned and secured behind the tip PCA opposite theresistors 60. This positioning may also be described as being positionedon the “back side of the support PCA opposite the resistor 60. In thisexemplary embodiment the dielectric cap 100 a (FIGS. 5 and 6) is used.As can be seen from FIG. 20, this placement of the lossy dielectric caphas a frequency response that is a significant improvement over thefrequency response (FIG. 2) of an exemplary test probe and that roughlyapproximates the frequency response (FIG. 4) of an exemplary test probewith a user's finger held over the resistors 60.

As shown in FIGS. 16-18, in a preferred embodiment a lossy dielectriccap 100 may replace the ferrite material 68 (such as that shown in FIG.3) with an alternative lossy dielectric cap 100. In the exemplaryembodiment of FIG. 16 the dielectric cap 100 b of FIG. 7 is used. In theexemplary embodiment of FIG. 17 the dielectric cap 100 d of FIG. 9 isused. In the exemplary embodiment of FIG. 18 the dielectric cap 100 e ofFIG. 10 is used. By increasing the size and/or positioning of thedielectric cap 100, these embodiments could be positioned along almostany point of a transmission path.

It should be noted that the specific embodiments of the lossy dielectriccaps shown in the various placements set forth above are meant to beexemplary. Alternative lossy dielectric caps could be positioned in eachof the various positions.

It should be noted that the present invention was described in terms ofand in relation to the shown exemplary test probe. It should be notedthat the present invention is not limited to this test probe.Alternative probes could have a single test probe tip. Alternativeprobes could have alternative bandwidths. Alternative test probes mightnot incorporate an amplifier near the probe tips.

It should be noted that the lossy dielectric cap of the presentinvention may be used with transmission paths that are not in a testprobe. For example, alternate transmission paths may be on a circuitboard, a hybrid circuit, or in any electric device where radiatedelectromagnetic fields may be problematic.

The terms and expressions that have been employed in the foregoingspecification are used as terms of description and not of limitation,and are not intended to exclude equivalents of the features shown anddescribed or portions of them. The scope of the invention is defined andlimited only by the claims that follow.

1. A lossy dielectric device for use with a transmission path, saiddevice comprising: (a) a container; (b) lossy dielectric materialcontained within said container; and (c) said container positionablesubstantially adjacent said transmission path to improve the curve of afrequency response.
 2. The lossy dielectric device of claim 1 whereinsaid container is insulative, puncture resistant, and thin.
 3. The lossydielectric device of claim 1 wherein said container is made of amaterial selected from the group consisting of: (a) plastic; (b) rubber;(c) polymeric material; and (d) biologically compatible elasticallydeformable material.
 4. The lossy dielectric device of claim 1 whereinsaid container has a structure selected from the group consisting of:(a) an at least partially flexible structure; (b) a completely flexiblestructure; and (c) a structure with a semi rigid bottom side and aflexible upper side.
 5. The lossy dielectric device of claim 1 whereinsaid dielectric material is selected from a group consisting of: (a) amixture of salt and water; (b) saline solution; (c) a polysiloxane or asilicone gel; and (d) bio-osmotic gel.
 6. The lossy dielectric device ofclaim 1 further comprising at least one connection mechanism selectedfrom the group consisting of: (a) at least one permanent connectionmechanism; and (b) at least one temporary connection mechanism.
 7. Thelossy dielectric device of claim 1 further comprising a layer of ferritematerial.
 8. The lossy dielectric device of claim 1, wherein said lossydielectric material is a lossy dielectric fluid, a “squishy” material,or a formable material enclosed in said container.
 9. A probing headcomprising: (a) a transmission path; (b) a container; (c) lossydielectric material contained within said container; and (d) saidcontainer securable substantially adjacent said transmission path toimprove the curve of a frequency response.
 10. The probing head of claim9 wherein said container is insulative, puncture resistant, and thin.11. The probing head of claim 9 wherein said container is made of amaterial selected from the group consisting of: (a) plastic; (b) rubber;(c) polymeric material; and (d) biologically compatible elasticallydeformable material.
 12. The probing head of claim 9 wherein saidcontainer has a structure selected from the group consisting of: (a) anat least partially flexible structure; (b) a completely flexiblestructure; and (c) a structure with a semi rigid bottom side and aflexible upper side.
 13. The probing head of claim 9 wherein saiddielectric material is selected from a group consisting of: (a) amixture of salt and water; (b) saline solution; (c) a polysiloxane or asilicone gel; and (d) bio-osmotic gel.
 14. The probing head of claim 9further comprising at least one connection mechanism selected from thegroup consisting of: (a) at least one permanent connection mechanism;and (b) at least one temporary connection mechanism.
 15. The probinghead of claim 9 further comprising a layer of ferrite material.
 16. Theprobing head of claim 9, wherein said lossy dielectric material is alossy dielectric fluid, a “squishy” material, or a formable materialenclosed in said container.
 17. A frequency response improving system,said system comprising: (a) a probing head; (b) a transmission pathassociated with said probing head; (c) a container; (d) lossy dielectricmaterial contained within said container; and (e) said containerpositionable and securable substantially adjacent at least part of saidtransmission path to improve the curve of a frequency response.
 18. Thesystem of claim 17 wherein said container has a structure selected fromthe group consisting of: (a) an at least partially flexible structure;(b) a completely flexible structure; and (c) a structure with a semirigid bottom side and a flexible upper side.
 19. The system of claim 17,wherein said lossy dielectric material is a lossy dielectric fluid, a“squishy” material, or a formable material enclosed in said container.20. A frequency response improving system for use with a probing headhaving a transmission path, said system comprising: (a) a container; (b)lossy dielectric material contained within said container; and (c) saidcontainer positionable and securable substantially adjacent at leastpart of said transmission path to improve the curve of a frequencyresponse.
 21. The probing head of claim 20 wherein said container has astructure selected from the group consisting of: (a) an at leastpartially flexible structure; (b) a completely flexible structure; and(c) a structure with a semi rigid bottom side and a flexible upper side.22. The system of claim 20, wherein said lossy dielectric material is alossy dielectric fluid, a “squishy” material, or a formable materialenclosed in said container.